1. Field of the Invention
The present invention relates to an antenna element for use in reception or transmission of radio waves, and more particularly, to an antenna element which has conductors formed on outer surfaces of a device substrate.
2. Description of the Related Art
At present, radio communication apparatuses called a mobile telephone and the like are pervasive in general users, and a reduction in size and weight is required for the radio communication apparatuses. The radio communication apparatus receives and transmits radio waves through an antenna element, where the total length of a conductive line is closely related to the wavelength of a radio wave transmitted or received thereby.
For this reason, since a simple reduction in the length of the conductive line causes a rise in the resonant frequency, difficulties are encountered in efficiently radio communicating a radio wave at a predetermined frequency. To address this problem, a variety of techniques have been devised for reducing the shape of an overall antenna element while maintaining a required resonant frequency.
For example, an antenna element called a helical antenna has a conductive line formed in a spiral shape, while an antenna element called a meander antenna has a conductive line in a meandering shape. While these antennas do not achieve a reduction in the total length of the conductive line, the overall shape can be substantially reduced.
There is also an antenna element called a dielectric antenna which has a conductive line formed on the surface of a dielectric material to reduce the length of the conductive line. Since the wavelength of a radio wave is reduced within a member having a high dielectric constant or permeability, the formation of the conductive line on or within a dielectric material or a magnetic material results in a reduction in the total length thereof.
Moreover, there is an antenna element called a loaded antenna which adds a reactance element, an inductance element or a capacitance element to a conductive line to reduce the length of the conductive line. It should be understood that a variety of foregoing techniques may be combined to create, for example, an antenna element which has a conductive line formed in a helical shape or in a meander shape on the surface of a dielectric material.
In another technique, a ground electrode is connected to a conductive line of an antenna element by a short pin to generate a current through the short pin in opposite phase to that in the conductive line in an opposite direction. Since the opposite phase current generated in the opposite direction in this manner can be regarded as an in-phase current generated in the same direction, a radiation resistance of the antenna element can be increased as a result.
A variety of techniques as described above permit an improvement in the performance of antenna elements without uselessly increasing the size thereof. However, in the helical antenna and meander antenna, a long conductive line is bent to reduce the area occupied thereby, so that adjacent portions of the conductive line are electromagnetically coupled to cause an increase in surface current and high frequency loss.
To solve the problem as mentioned, the present inventor invented an antenna element which has a conductive line formed in a shape different from the helical shape or meander shape on the surface of a dielectric material, and filed the invention as Japanese Patent Application No. 2001-026002. This application discloses an antenna element which has a first conductor and a second conductor, parallel to each other, connected by a short-circuit conductor to form a loaded inductance.
Referring now to FIGS. 1 and 2, the antenna element disclosed in the above-cited application will be described below in brief, as a related art which precedes the present invention and is not known. The antenna element described below was filed in Japan on Feb. 1, 2001 as Japanese Patent Application No. 2001-026002, and filed in the United States of America on Jan. 31, 2002 as U.S. Ser. No. 10/059423 by the present inventor. However, this application has not been opened in any country, so that this is not a prior art but merely a related art of the present invention.
Antenna element 100 in the aforementioned application has device substrate 101 made of a dielectric material, and conductive line 102 formed of a printed wire on a front surface and a bottom surface of device substrate 101. Conductive line 102 is comprised of power supply conductor 103, first conductor 104, short-circuit conductor 105, and second conductor 106, each of which is linearly formed in succession.
More specifically, power supply conductor 103 of conductive line 102 comprises a linear portion formed from the bottom surface to the front surface of device substrate 101, while first conductor 104 comprises a linear portion formed from an upper end which is a terminate end of power supply conductor 103 and bent at a right angle to the right in the figure. Short-circuit conductor 105 comprises a linear portion formed from a right end which is a terminate end of first conductor 104 and bent upward at a right angle in the figure, i.e., in the opposite direction to power supply conductor 103, while second conductor 106 comprises a linear portion formed from an upper end which is a terminate end of short-circuit conductor 105 and bent at a right angle to the left in the figure, and positioned in parallel to first conductor 104.
Then, antenna apparatus 200 using antenna element 100 as described above comprises a circuit board 201 made of glass epoxy resin, ethylene tetrafluoride or the like, as illustrated in FIG. 2. A copper foil is adhered in a lower half and the like of a front surface of circuit board 201 to form a ground electrode 202.
Ground electrode 202 is partially formed with a recess in which power supply electrode 204 is formed for power supply circuit 203 (for example, a coaxial cable) which serves as a power supply means. Then, antenna element 100 is mounted on an upper half of the front surface of circuit board 201 on which ground electrode 202 is not formed. Power supply conductor 103 is connected to power supply electrode 204.
In antenna element 100 of the structure as described above, conductive line 102 can be reduced in length since first conductor 104 and second conductor 106, positioned in parallel to each other, act as a loaded inductance. In addition, since conductive line 102 is generally bent in an inverted C-shape, the overall shape can be reduced in size.
Unlike the meander antenna, helical antenna and the like, in spite of the reduction in size, first conductor 104 and second conductor 106, positioned in parallel to each other, are sufficiently spaced away from each other, so that their electromagnetic coupling is reduced, thereby making it possible to realize radio communications with a high gain, high efficiency and wide band.
In antenna element 100, since short-circuit conductor 105 mainly transmits and receives radio waves, the transmission/reception have a directivity in the horizontal direction in the figure orthogonal to the longitudinal direction of the short-circuit conductor 105. For this reason, if a conductor such as ground electrode 202 is positioned in a direction orthogonal to short-circuit conductor 105, the conductor will impede the transmission/reception of radio waves through short-circuit conductor 105.
To solve the foregoing problem, it is contemplated to avoid forming ground electrode 202 and the like in the direction orthogonal to short-circuit conductor 105. However, this solution would cause a reduction in the area of ground electrode 202 available for mounting circuit parts (not shown). In other words, it is necessary to minimize an antenna mounting area on which ground electrode 202 is not formed in order to maximize an area available for mounting circuit parts.
It is an object of the present invention to provide a highly efficient antenna element which is capable of minimizing an antenna mounting area in a structure which has a first conductor and a second conductor positioned in parallel to each other and connected through a short-circuit conductor.
Similarly to the aforementioned related art, an antenna element of the present invention includes a device substrate and a conductive line which is comprised of at least a power supply conductor, a first conductor, a short-circuit conductor, and a second conductor. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the power supply conductor, first conductor, short-circuit conductor, and second conductor. The power supply conductor is made of a linear conductor, and supplied with electric power at a leading end thereof. The first conductor is connected to a terminate end of the power supply conductor at a right angle, while the short-circuit conductor is connected to a terminate end of the first conductor at a right angle on the opposite side of the power supply conductor. The second conductor is connected to a terminate end of the short-circuit conductor at a right angle, and positioned in parallel to the first conductor.
In the antenna element of the present invention as described above, the device substrate is also formed with a ground conductor which has a terminate end connected to the conductive line, and a leading end applied with a ground potential.
Since this structure allows the ground conductor to function in a manner similar to a conventional short-pin, the antenna element can have an increased radiation resistance. Also, impedance matching can be adjusted by changing reactance and/or resistance of input impedance of the conductive line. The resonance frequency can also be adjusted by a position at which the ground conductor is connected to the conductive line. Further, the performance can be improved in the antenna element which includes a loaded inductance formed of the parallel first and second conductors.
In another implementation of the antenna element as described above, a capacitive conductor having a given capacitance is formed as part of the conductive line, and connected to a terminate end of the second conductor. Thus, the conductive line can be reduced in length by a loaded capacitance of the capacitive conductor, so that the antenna element can be reduced in size.
The ground conductor has a terminate end electromagnetically coupled to the conductive line in non-contact manner. Since the electromagnetic coupling eliminates the need for directly connecting the ground conductor to the conductive line, the ground conductor can be readily formed.
A first antenna apparatus according to the present invention includes an antenna element, a circuit board, a ground electrode, and a ground wire. The antenna element includes the antenna element according to the present invention, and the circuit board has the antenna element mounted on a front surface thereof. The ground electrode is formed at a position spaced apart from the antenna element on the front surface of the circuit board for generating a ground potential. The ground wire is formed on the front surface of the circuit board, and has a leading end connected to the ground electrode, and a terminate end connected to a leading end of the ground conductor.
A second antenna apparatus according to the present invention includes a device substrate, a conductor line, a circuit board, a ground electrode, and a ground wire. The conductive line is comprised of a power supply conductor, a first conductor, a short-circuit conductor, and a second conductor. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the power supply conductor, first conductor, short-circuit conductor, and second conductor. The power supply conductor is made of a linear conductor, and is supplied with electric power with a leading end thereof. The first conductor is connected at a right angle to a terminate end of the power supply conductor, while the short-circuit conductor is connected at a right angle to a terminate end of the first conductor on the opposite side of the power supply conductor. The second conductor is connected at a right angle to a terminate end of the short-circuit conductor, and positioned in parallel to the first conductor. The circuit board is mounted with the device substrate on a front surface thereof. The ground electrode is formed at a position spaced apart from the device substrate on the front surface of the circuit board for generating a ground potential. The ground wire is formed on the front surface of the circuit board, and has a leading end connected to the ground electrode, and a terminate end connected to a leading end of the ground conductor.
In the antenna apparatus of the present invention configured as described above, since the ground potential at the ground electrode is applied to the ground conductor of the antenna element through the ground wire, the ground conductor of the antenna element can function in a manner similar to a conventional short pin.
In another implementation of the antenna apparatus as described above, a capacitive conductor having a given capacitance is connected to a terminate end of the second conductor and additionally formed as part of the conductive line. Thus, the conductive line can be reduced in length by a loaded capacitance of the capacitive conductor, making it possible to reduce the antenna apparatus as well as the antenna element in size.
Also, since the ground conductor has a terminate end electromagnetically coupled to the conductive line in non-contact manner, the ground conductor need not be directly connected to the conductive line. Consequently, the ground conductor, for example, may be formed only on the front surface of he circuit board without extending to the antenna element, thereby facilitating the formation of the ground conductor.
A third antenna apparatus according to the present invention includes a conductive line, a device substrate, a circuit board, a ground electrode, a power supply electrode, and a ground wire. The device substrate is made of at least one of a dielectric material and a magnetic material, and is formed with the conductive line. The circuit board is mounted with the device substrate on a front surface thereof. The ground electrode is formed at a position spaced apart from the device substrate on a front surface of the circuit board for generating a ground potential. On the front surface of the circuit board, the power supply electrode has a terminate end connected to the conductive line on the device substrate, and is supplied with electric power at a leading end. The ground wire, which is formed on the front surface of the circuit board, has a leading end connected to the ground electrode, and a terminate end connected to the power supply electrode.
As appreciated from the foregoing, since the ground potential at the ground electrode is applied to the power supply electrode through the ground wire in the antenna apparatus according to the present invention, the ground wire functions in a manner similar to a conventional short pin. In addition, the present invention can provide a reduction in the entire size of the antenna apparatus, as well as a wider bandwidth and a higher efficiency for the same.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.